1. Field of the Invention
The present invention relates to a voltage divider circuit in a semiconductor device.
2. Description of the Related Art
A voltage divider circuit formed on a semiconductor integrated circuit needs to be adjusted in resistance by providing an adjustment circuit when there is a fluctuation in resistance due to a manufacturing process or when high precision is required. The resistance is adjusted by trimming using a fuse or the like.
To achieve high precision, however, the adjustment circuit has a larger area and a larger number of resistors, leading to an increased area. There is another problem that the trimming does not result in the same output voltage because a combined resistance of the voltage divider circuit is not constant. To address the problems, there has been developed a technology in which the combined resistance after trimming is kept constant and the number of resistors is reduced (see Japanese Patent Application Laid-open No. 2007-233922).
FIG. 2 illustrates a circuit diagram of a conventional voltage divider circuit. In a voltage divider circuit 1, a first resistor circuit 2 and a second resistor circuit 3 are provided in series between a voltage V1 and a voltage V2 to output a divided voltage V3 from a connection node thereof. Adjustment resistors Ra1 to Ran and adjustment resistors Rb1 to Rbn each have a resistance weighted in binary code. For example, when the adjustment resistor Ra1 has a resistance of K, an arbitrary adjustment resistor Rai (i=1 to n) has a resistance of K×2i−1. Between the first resistor circuit 2 and the second resistor circuit 3, corresponding resistors have the same resistance. The voltage divider circuit 1 is designed such that a combined resistance of the first resistor circuit 2 and the second resistor circuit 3 after trimming becomes constant (K×7).
When configured as described above, the voltage divider circuit 1 can always have a constant combined resistance of the first resistor circuit 2 and the second resistor circuit 3 after trimming, and accordingly the necessary numbers of resistors and fuses can be significantly reduced as compared with a conventional voltage divider circuit. Further, in a circuit in which voltage setting is made by varying the resistances, voltage drop due to a resistor does not change, and hence as long as the same voltage is input from the outside, the same voltage can be set even in a constant voltage circuit or a voltage detection circuit having any configuration.
In the above-mentioned voltage divider circuit, however, the two same resistors need to be prepared at a time to keep constant the combined resistance of the first resistor circuit 2 and the second resistor circuit 3 after trimming. Therefore, two resistors with the largest size are necessary as well, which is a disadvantage that the area is increased when the resistance is large.